1. Field of the Invention
The present invention relates to an additive for fluxes and soldering pastes, a flux containing the additive and a soldering paste containing the flux. In the field of electronics, fluxes are widely used for the purpose of removal of an oxide film on a metallic base. The flux of the present invention is the novel flux which never corrodes metallic bases even though it remains on the metallic bases after soldering.
2. Description of Prior Art
In a general method for soldering electronic parts on a metallic base (for example, copper base) for electronic circuits, a surface of the base is treated with a flux to remove an oxide film and then the surface is dipped into a melted solder bath. However, this method requires two steps: (1) treatment with the flux and (2) dipping into the solder bath. Further, in this method, some of the electronic parts put on the base have removed occasionally from the base in the course of the steps.
In order to solve these problems, the method using a soldering paste containing a flux and solder particles has been developed. According to the method, the soldering paste is applied on a base by, for example, a dispenser and then heated or irradiated with ultraviolet light to complete soldering. Since the soldering paste is viscous, electronic parts are easily held on the base. However, even the above method has some disadvantages. The soldering paste contains an activator such as organic acids and organic acid salts in order to remove an oxide film on the base perfectly. After soldering, the soldered base has to be washed to remove the activator because the corrosion of the base with the remaining activator continues after completion of the soldering operation.
In general, a solvent of fluorohydrocarbons such as Freon and water are used for this washing. However, the use of fluorohydrocarbons tends to be prohibited because they have harmful effects on the atmospheric environment. Further, if water is used for the washing, the resulting waste water is polluted with heavy metals and cannot be discharged without removal of the metals.
Therefore, an object of the present invention is to provide a soldering paste which contains an activator and does not continue to corrode a base after soldering even though the soldered base is not subjected to a washing step.
Another object of the present invention is to provide a flux which contains an activator and does not continue to corrode a base after soldering even though the flux is contained in a soldering paste and the base soldered with this paste is not subjected to a washing step.
A further object of the present invention is to provide an additive for a flux and a soldering paste containing an activator, which is contained in the flux and the soldering paste and deactivates the activator in the course of soldering.